A number of fluorescence detection techniques are available based on registering single photons. Such techniques are commonly referred to as single photon detection (SPD) techniques. Because of their complexity and cost, in biomedical applications single-photon detection techniques are mostly used for time resolved fluorescence spectroscopy or detection of single fluorescent molecules.
As shown in the block diagram of FIG. 1, the conventional single photon detector heretofore consisted of several modules including a single photon sensor or photo-multiplying tube (PMT) detector, a pulse amplifier, a pulse shaper, a counter, and a computer. A factor impeding the performance of single photon detectors heretofore is the relatively narrow linearity dynamic range of available photon counting devices. A detector's dynamic range is determined by the response time, τRESPONSE, needed for the detector to respond to a single photon. The quantity τRESPONSE depends on the response times of all of the modules of the device and is generally considered to be the sum of response times of the individual modules. As shown in the graph of FIG. 2, in practice the shortest response time in currently available single photon sensors is about Ins. However, conventional single photon PMT detectors with a given τRESPONSE, have heretofore been limited to a dynamic range of 106-107 photocounts per second.
In biological applications, and in particular in DNA detection, DNA sequencing systems have heretofore been unable to process and detect ultra-high speed DNA sequencing. In fact, conventional DNA sequencers have been limited to a recording sequencing process at 10-30 frames per second. Moreover, the dynamic range of conventional DNA machines has been limited to 16 bit. Conventional equipment for serial dilutions of BigDye DNA sequencing standard have heretofore been relatively insensitive by at least a factor of 10 less than what is desirable.
Accordingly, there is a need for sensors including single photon detectors with photon counters having linearity range exceeding 107 photocounts per second, for example up to 108 photocounts per second, DNA sequencing processing capability of greater than 10-30 frames per second and a far more sensitive BigDye DNA sequencing standard. Spectrometers based upon multi-channel single photon detectors, for example based upon a 32-channel PMT sensor, would enable a very accurate, high speed detection of multi-color radiation. In particular, such detectors would demonstrate highly accurate and fast recognition of combinations of fluorescent moieties, and high quality detection of DNA sequencing.